In general, reinforced concrete is an excellent material, making it possible to obtain structures having a lifetime of forty years and more provided the integrity of the material is conserved. To achieve this, it is necessary to ensure that the specifications concerning the type of cement, its proportions, the compactness of the concrete, the quality of the aggregate, and the thickness of the covering overlying the reinforcement are all satisfied.
However, corrosion may develop under conditions that are particularly aggressive for the material, such as sea water, where the presence of defects facilitates degradation of the concrete and of its reinforcement. It is therefore necessary to be able to monitor the corrosion state of the reinforcement using a methodology appropriate to obtaining as accurate a diagnosis as possible.
When a concrete structure stands in air, the commonly used method of detecting corrosion consists in measuring so-called "electrode potential". The principle consists in measuring the potential difference between the reinforcement latticework of the concrete and a reference electrode placed on the facing of the concrete. In order to locate zones of active corrosion, it is necessary to take a large number of measurements at points in a net of greater or lesser mesh size. The method is flexible in use: the apparatus is simple and suitable for connection to a data acquisition system, and in most cases measurements can be performed quickly. The main problems encountered are related to the dryness of the concrete. Too low a water content in the concrete makes the values unstable.
For moderately dry concrete in air, the measured electrode potential corresponds to a point immediately under the reference electrode. When the concrete is underwater, the measured electrode potential corresponds to a region of reinforcement adjacent to the electrode, and in addition, the presence of water around the electrode and having a greater or lesser air content disturbs the measurements and makes them unreliable.
An object of the present invention is to provide a device of the type specified above and capable of obtaining reliable measurements even when the electrode is disposed close to the reinforcement of underwater concrete.